1). Field of the Invention
This invention relates to an electronic assembly of the kind having a semiconductor package substrate which is attached to a printed circuit board.
2). Discussion of Related Art
A semiconductor die having an integrated circuit formed therein is often mounted on top of a package substrate. The integrated circuit is electrically connected through contact pads on an upper surface of the package substrate and metal lines in the package substrate to contact pads on the lower surface of the package substrate. A respective solder ball is attached to a respective one of the contact pads on the lower surface of the package substrate. The solder balls are located in an array in a horizontal plane.
The solder balls are subsequently located on contact terminals on an upper surface of a printed circuit board. The solder balls are then heated to above their melting temperature, so that they reflow over the contact terminals on the printed circuit board. Subsequent cooling and solidification of the solder balls secures them to the contact terminals.
The package substrate usually collapses toward the printed circuit board when the solder balls reflow. There has in the past been no need to minimize such collapsing, because collapsing did not directly influence structural or electrical cooperation between the printed circuit board and the package substrate.